Provided are processes for the preparation of lyophilized pharmaceutically acceptable salts of pemetrexed diacid, in particular, pemetrexed disodium salt, directly from pemetrexed diacid or salts thereof, i.e., without isolating the obtained pemetrexed salt prior to lyophilizing it.本發明提供直接自培美曲塞二酸(diacid pemetrexed)或其鹽,亦即,在將其冷凍乾燥之前不分離該所獲得之培美曲塞鹽,來製備培美曲塞二酸之冷凍乾燥醫藥學上可接受之鹽,特定言之培美曲塞二鈉鹽的方法。